Computing circuit for determining bomb release points



aaa-wl SR Nov. 15, 1949 c. H. TOWNES ET AL 2,438,448

COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE POINTS Original Filed July 17, 1943 6 Sheets-Sheet 1 FIG. .5

c. H. TOWNES WI/ENTQPS 0. E. WOOLDR/DGE ATTORNEY 6 Sheets-Sheet 2 SIl/FTER 90 PHASE lllllllllmm 17 BOMB RELEASE POINTS FIG. 7

C. H. TOWNES ET AL COMPUTING CIRCUIT FOR DETERMINING Nov. 15, 1949 Original Filed July 17, 1945 C. H. TOWNES' D. E. WOOLDR/DGE ilk'flu dk.

ATTORNEY IN l E/V TORS Nov. 15, 1949 c. H. TOWNES ETAL COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE POINTS 6 Sheets-Sheet 4 Original Filed July 17, 1943 c. H. row/v55 MFA/mp5- 0. E. woman/0a:

i- *L-Mdt ATTORNEY Nov. 15, 1949 c. H. TOWNES ET AL 2,488,448

COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE POINTS Original Filed July 17, 1945 6 Sheets-Sheet 5 Wy .S/N 5 3/4; -I? S/N 8 +5 SW A 3/5 c. h. TOWNES WI/ENTOAS- 0. E. woowmoas A T TOR/V5 Y Nov. 15, 1949 c. H. TOWNES ET AL 2,488,448

COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE POINTS 64s FILLED C- H. TOWN'S INVENTORS. D. E. WOOLDR/DGE A 7'70/QNE Y Patented Nov. 15, 1949 UNITED STATES PATENT OFFICE COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE POINTS Original application July 17, 1943, Serial No. 495,130, now Patent No. 2,439,381, dated April 13, 1948. Divided and this application April 27, 1945, Serial No. 590,605

7 Claims. (Cl. 235-615) This invention relates to a computer associated with an aerial bombsight, and particularly to a computer in which the data are represented in the form of electrical quantities.

This application is a division of United States application, Serial No. 495,130 filed July 17, 1943, by S. Darlington, 0. H. Townes and D. E. Wooldridge, now Patent No. 2,439,381, issued April 13, 1948.

The object of the invention is a method and means for indicating the correct course to be flown by an aerial vehicle, and for releasing the bomb automatically at the correct point, so that the bomb will fall on a target.

A feature of the invention is the derivation from the smoothed electrical quantities representing the components of the ground speed of the vehicle, of other electrical quantities that make possible a comparison of the ratio between the deflection component of the horizontal ground speed and the range component of the horizontal ground speed and the ratio between the deflection component of the displacement of the plane from its predicted position at the instant of impact and the range component of the same displacement; and the comparison of these electrical quantities, whereby equality of these quantities indicates the correct track to be flown by the aerial vehicle. The ground speed is really the speed of the airplane with respect to the target, which may or may not be stationary.

Another feature of the invention is the derivation, from the smoothed electrical quantities representing the components of the ground speed with respect to the vertical plane through the vehicle and the target, of another electrical quantity representing the component of the ground speed normal to the head to tail axis of the vehicle, the fractionation of this latter quantity proportionally to the ratio of the trail of the bomb to the horizontal range to the target, and the comparison of this fractionated quantity with the quantity representing the component of the ground speed normal to the vertical plane, whereby equality of these quantities indicates the vehicle is on the correct course to bomb the target.

A further feature of the invention is the derivation from the smoothed electrical quantities representing the constant velocity components of electrical quantities proportional to the range component of the displacement of the aerial vehicle from its predicted position at the instant of impact of the bomb, and of electrical quantities proportional to the range component of the displacement of the aerial vehicle during the pre- 2 dicted. time of fall of the bomb, and the comparison of these electrical quantities, whereby equality of these quantities indicates the correct time to release the bomb and automatically controls the release thereof.

The present computer is associated with a bombsight capable of continuously measuring an azimuth angle and a distance. The azimuth angle is measured from some assumed vertical plane at the aerial vehicle to the vertical plane through the line of sight. The reference plane may conveniently be taken to be the vertical plane that includes the head to tail axis of the aerial vehicle, and the azimuth angle may be measured clockwise. The distance is the slant distance from the vehicle or airplane to the tar get. The bombsight may be an optical instrument including a theodolite for measuring the azimuth angle and an optical range finder for measuring the distance, a radio locating equgp;

ment capable of measuring the azimuth angle and slant distance or a combination of optical and radio devices. The range finder may also be used to measure height or elevation of the airplane above the surface of the earth. The measurement of height, and the continuous measurements of azimuth angle and slant distance are supplied as voltages to the computer, together with information in the form of voltages representing the vector velocity of the airplane with respect to the air and the ballistic characteristics of the bomb used, and the computer continuously indicates the correct course to be flown, and finally operates release mechanism at the correct instant to drop the bomb so as to strike the target.

The operation of the computer will be better understood from the drawings, in which:

Fig. 1 shows the geometrical relationships, projected on a horizontal plane through the vehicle;

Fig. 2 shows the geometrical relationships, projected on a vertical plane through the vehicle and the target;

Fig. 3 diagrammatically shows the vector and component velocities involved in Fig. 1;

Fig. 4 shows the geometrical relationships of Fig. l at the instant of release of the bomb;

Fig. 5 shows the velocity relationships of Fig. 3 at the instant of release of the bomb;

Fig. 6 diagrammatically shows a radio locator associated with the computer;

Fig. 7 schematically shows a device for producing a rotation proportional to horizontal range;

Fig. 8 shows a summing amplifier forming part of the device shown in Fig. 7;

Fig. 9 schematically shows a device for producing a rotation proportional to the difference between the angles and A;

Figs. 10, 11 and 12 schematically show the computing elements forming part of the invention;

Fig. 13 schematically shows a summing amplifier forming part of Figs. 10, 11, 12;

Figs. 14 and 14A schematically show the circuit for the steering meter; and

Fig. 15 schematically shows the circuit for releasing the bomb.

In Fig. l, P represents an aerial vehicle, such as an airplane, headed along the course PA. Assume, as usual in bombing technique that the airplane is filying at constant speed and at constant height. If a wind be blowing with respect to the target, the airplane will actually travel along a truck such as PB. The target is located at O, and the function of the present invention is to indicate the correct track PB, and the correct release point RP so that the bomb will fall on the target.

In Fig. 2, the constant height H of the airplane is PD, the constantly measured slant distance p is PO. From these two measurements, the computer can continuously compute the distance D0, which is the horizontal range R, represented by P0 in Fig. 1.

If PA is a correct bombing course, and the airplane steadily heads along the course PA at constant speed and height, releases a bomb at RP, and continues at the same speed along the track PB, it will reach the point B at the time of impact. The distance OB, along the fore and aft axis of the airplane is known as the trail T, and is tabulated in the ballistic tables for the type of bomb used.

The angle APO- between the course of the airplane and the vertical plane through the target is designated 0. If the air structure is standard, the bomb will fall directly behind the airplane, in the vertical plane including the head-to-tail axis of the airplane, that is, the trail is in the line of the course, so that angle BOC=angle APC=0. Thus, DC, the range component of the trail equals T cos 0 and BC, the deflection component of the trail equals T sin 0. The distance PC equals R+T cos 0.

The airplane is equipped with a gyroscopic device, such as the device shown in United States Patent 1,959,803, May 22, 1934, B. A. Wittkuhns, which maintains an axis PX having a direction fixed in space and is equipped with a servomotor which indicates the angle A between this axis and some fixed axis of the airplane which may conveniently be the head to tail axis of the airplane lying in the course of the airplane.

The azimuth angle 0 is continuously measured by the observing equipment, thus, the angle 6, between the axis fixed in direction and the vertical plane containing the airplane and the target, which is equal to 0-7\ may be determined.

The relative velocity between the airplane and the target, which may be termed the ground speed is indicated by the vector V, Fig. 3. This vector V may be resolved into a component -R in the vertical plane containing the airplane and the target. This component is the rate of change in the horizontal range R, indicated by the dot, and as the range is decreasing is inherently a negative quantity. The vector V is also resolved into the component GF, equal to Rt, where S is the rate of change in 6. (This resolution of vectors is shown in section '7, page 11, of The Dynamics of Particles, A. G. Webster, 1912, published by G. E. Stechert and Company, New York.)

In Figs. 1 and 3, the triangles BPC and FPG are similar, thus,

@i T sin 0 R R+ T cos 0 This equation may be multiplied by R(R+ T cos 0) R and rearranged to give In Equation 1, the quantity R5 is the component of the ground speed V normal to the vertical plane through the airplane and target, the quantity R5 cos 0+R sin 0 is equal to the component of the ground speed normal to the head to tail axis of the airplane, and the quantity is the ratio of the trail of the bomb to the horizontal range from the vertical projection of the airplane to the target.

If a voltage varying in proportion to the lefthand side of Equation 1 be produced and applied to a meter, the needle of the meter will be in the center of the scale when the airplane is on the correct track; when the airplane is to the right of the correct track the needle will be deflected to the left of the center of the scale; when the airplane is to the left of the correct track the needle will be deflected to the right of the center of the scale. The needle of the meter thus indicates in which direction the airplane should be turned to come back to the correct track.

Fig. 4 shows the relationship of Fig. 1 at the instant the airplane passes through the release point RP. The condition defining a correct release point is that if the plane continues after releasing the bomb along the same track at the same velocity for a time equal to the time of fall if of the bomb it will just reach a point at a horizontal distance from the target, measured along the line of the course equal to the trail T.

In Fig. 4, as in Fig. 1, angle BCO is a right angle. Then, as before, the distance RPC equals R+T cos 6. The distance RPB is the distance the airplane travels at a velocity V during the time of fall if of the bomb and evidently equals Vt. In Fig. 5 the velocity of the plane V is represented by the vector RPB, and the range component of this velocity -R is represented by the vector RPC. In Figs. 4 and 5 the triangles RPBC are similar. Thus lj R+ T cos 0 V Vt and

R+Tcos0+Rt=0 2 The expression R+T cos 0 is termed the range component of the displacement of the vehicle from its predicted position at the instant of impact of the bomb, and the expression R1. is the range component of the displacement of the vehicle during the predicted time of fall of the bomb. During the bombing run R+T cos 0 is larger than Rt, until, at the correct release point RP, these quantities become equal. Thus, if a voltage varying in proportion to the left-hand side of Equation 2 be produced, and supplied to a meter this voltage will fall to zero at the correct time to release the bomb.

The angle 6 is measured with respect to an axis having a direction fixed in space, thus Equation 1 is valid for any course curved or straight. The voltage proportional to Equation 2 decreases as the airplane approaches the release point, and falls to zero at the release point. Thus, during the bombing run, the pilot may fly on any course at the measured height, and the steering meter will indicate the direction to be steered to come to the correct track, while the release meter indicates the time before reaching the correct release point. A convenient time before reaching the release point, the pilot steers to the correct track and follows this track when passing through the release point. After the bomb is released, the pilot may fly on any desired course.

In following a moving target, an observer will tend to overrun and underrun the target with his tracking device, thus introducing errors and irregularities in the data furnished to the computer. To make an accurate determination of R and R6 the derived ratio must be averaged or smoothed. It is very difiicult to smooth the measured values of a quantity such as R or R6, the correct value of which is varying. Therefore, in accordance with the present invention, the observed positional data are operated upon so as to yield expressions for velocity components which are inherently constant, and these quantities are averaged. The observed positional data are operated upon to give the components, parallel and perpendicular to the fixed axis, of the vector velocity of the air with respect to the target. This vector velocity is constant during the bombing run and is therefore appropriate for averaging.

In Fig. 3 the vector S is the vector velocity of the airplane with respect to the air, measured along the course, or head-to-tail axis of the airplane, by known means, such as a Pitot tube device.

The vector W represents the vector velocity of the air with respect to the target, which is the vector velocity of the wind with respect to the ground minus the vector velocity of the target with respect to the ground.

The vector V represents the vector velocity of the airplane with respect to the target.

These three vectors are not independent but satisfy the relation Taking the ac axis along PX, the axis fixed in space by the gyroscope, and the y axis normal to PX, the vector S may be resolved into the components Sy=S sin A, in which +S cos A is the component of the airspeed along the fixed axis, and S sin A is the component of the airspeed transverse to the fixed axis.

In deriving Equation 1, the vector V was resolved into a vector PG designated R, and a vector GF, designated R6. In Fig. 3, GM and EN are normal to the fixed axis, and FL is normal to GM, thus FL equals MN. The angle PGM equals W, S cos )v-R cos 6+R6 sin 6 (3) W,,=S sin x-R sin 6R8 cos 6 (4) or, in the equivalent form,

(1 -W,=s cos cos d W,, +S sin )w-a' $111 where d a (R cos 6) is the ground speed along the :1: axis, and

uz sin a) is the ground speed transverse to the :c axis.

The values of Wx and Wy are averaged for the time of the bombing run, and in the averaging process the data are weighted in proportion to the accuracy of the measurements. Let the ay e raged values of these components be Wx and Wy.

From Equations 3 and 4 where R and R6 are subject to the low inaccuracies of the weighted time averages of Wx and Wy, and may be used in the computation of the correct course and release point by Equations 1 and 2.

The present device requires voltages proportional to the slant distance from the airplane to the target, and to the azimuth angle from the reference vertical plane to the vertical plane through the airplane and the target. Many known devices may be adapted to supply these voltages. A potentiometer may be mounted on an optical range finder, and the wiper moved in accordance with the movements of the range indicator to select a voltage proportional to the slant distance measured by the range finder. Another potentiometer may be mounted concentrically with the vertical axis of a theodolite sighted on the target, and the wiper moved in accordance with the rotation of the theodolite to select a voltage proportional to the angle turned by the theodolite. Or, as shown in Fig. 6, a radio locator of any suitable type, such as shown in British Patent 535,120, March 28, 1941, Compagnie Generale de Telegraphie Sans Fil, may be adapted to supply these voltages. In this particular locator, the range is indicated by the location of a bright spot on the surface of a cathode ray oscilloscope H). A worm shaft ll, rotated by a hand wheel I2, or by a suitable motor, drives a nut I3 carrying a pointer H which is kept aligned with the bright spot on the oscilloscope. The winding I9 of a potentiometer is R S cos 0-1-1 1 cos 6-1-1 1 sin 6 E6=S sin 0l7 sin 6-HT, cos 6 1 mounted below the worm shaft H, the wiper l5 of the potentiometer being mounted upon, but insulated from the nut l3. A suitable source of voltage may be connected to the terminals l6, l1, and the wiper I may be led out to a terminal I8. The antennas and reflector 2|], 2| of the radio transmitter and receiver may be supported by a framework mounted on a shaft 22 journalled in a support 23 rotatably mounted in a base 24. The hand wheel 25, bevel gears 26 and gear 21 drive the gear 28 rotating the antennas in azimuth. A potentiometer winding 29 may be mounted upon the base 24 but insulated therefrom, and connected to the terminals 30, 3|. A wiper 33 may be mounted upon the support 23 but insulated therefrom and connected to a terminal 32. The voltage selected by the wiper 33 will then be proportional to the azimuth angle. While, for the sake of explanation, one specific type of locator has been illustrated it is evident that the present invention is not limited to use with such a device, but will operate with many optical, mechanical, radio, sonic and other devices.

In Fig. 7 voltage from a suitable source 35 is applied to the terminals I6, ll of the winding l9 associated with the range indicator in Fig. 6. Voltage from the source 36 is applied to the windings 3'! and 38 of two other potentiometers. The windings I9, 31, 39 have a resistance per unit length varying linearly with the wiper displacement, so that the voltages selected by the wipers l5, 39, 40 are proportional to the square of the distance moved by the wipers.

The voltage selected by the wiper I5 is, as indicated, of the opposite polarity to the voltages selected by the wipers 39, 40.

The wiper 39 is set at the measured value of the height of the airplane.

The voltages selected by the wipers 39, 40 which are respectively equal to +11 the square of the height or altitude of the airplane, and approximately equal to +R the square of the horizontal range, and the voltage from the wiper l5 which, due to the reversal of polarity, is proportional to -p the negative square of the slant distance, are respectively supplied to a summing amplifier 4|, which may be of the type shown in Fig. 8.

It will be noted from Fig. 2 that H and R are the sides of a right triangle, of which p is the hypotenuse, thus H +R p should equal zero.

If the voltages summed up by the amplifier 4| are not equal to zero, the relay 42 will be operated. The relay 42 is a polar relay, normally biased to a central position, and moved in one direction or the other depending upon the polarity of the applied voltage.

The relay 42 controls the supply and phase of alternating current from the source 43 to one phase of the two-phase motor 46, the other phase of the motor 46 being supplied from the source 43 through the 90-degree phase-shifting network 44. When the relay 42 is operated the motor 46 is started, rotating in a direction related to the polarity of the voltage applied to relay 42. The wiper 40 is moved by the shaft of the motor 48, either directly or through suitable gearing, flexible shafting or other mechanical expedient. The movement of the wiper 40 changes the voltage selected by the wiper 40 until the voltage in the output of amplifier 4| is reduced to zero and relay 42 is released. Under this condition and the movement of the wiper 40 indicates the value of R, the horizontal range. Other potentiometers may be mounted so that their wipers will 8 also be rotated by the motor 46 an amount proportional to R.

The summing amplifier 4| of Fig. 7, which is shown in Fig. 8 may include any desired number of stages of amplification. Any suitable vacuum tubes may be used, though pentode tubes, or other tubes of high gain, will generally be found most eflicient. The heaters are supplied with power in known manner (not shown) The resistors 41, 48, 49 are connected to the control electrode of the vacuum tube 50, the terminal 5| being grounded. The first stage vacuum tube 50 may conveniently be a single cathode double triode, though two separate tubes of any suitable type may be used. The cathode of the vacuum tube 50 is connected to a resistor 52 of fairly high resistance, say of the order of one or two hundred thousand ohms. The anode current flowing in the resistor 52 would tend to make the cathode of the vacuum tube 50 positive with respect to ground. A source of voltage 53, having the negative pole connected to the resistor 52, and the positive pole connected to ground on terminal 5|, compensates for the voltage drop in resistor 52, so that the cathode of the vacuum tube 50 is at substantially ground potential. Since the total space current leaving the cathode is very nearly equal to the quotient of the voltage of 53 and the resistance of 52, their relative values must be chosen so as to give reasonable current values in the triodes used.

The double triode 59 is connected so as to reduce drift due to variations in cathode activity as described in an article Sensitive D. C. amplifier with A. C. operation, by S. E. Miller, published in Electronics, November, 1941, page 27.

The upper section of the twin triode 50 is coupled to the vacuum tube 54 by an interstage coupling network of the type shown in United States Patent 1,751,527, March 25, 1930, H. Nyquist, including the resistors 56, 51, 58 and a source of voltage 55 having the positive pole connected to resistor 56, the negative pole connected to resistor 58 and an intermediate point connected to ground. The resistor 56 may be adjustable to assist in making the potential of the cathode of vacuum tube 50 equal to ground potential.

The vacuum tube 54 is coupled by a similar interstage coupling network to the vacuum tube 60.

Current from a source 6| is supplied through resistor 62 to the anode of vacuum tube 60, returning through the cathode to the source 6|.

The wipers I5, 39, 40, Fig. 7, are respectively connected to resistors 41, 48, 49 and the winding of relay 42 is connected to terminals 63, 64.

The source 6| tends to maintain the terminal 63 at a potential positive with respect to ground. This potential is opposed by a potential from the source 65 through the winding of relay 42 so that, in the absence of an applied signal, the terminals 63, 64 are at the same potential, that is, there is no potential difference applied to the winding of the relay 42, Fig. 7. Assume that a voltage is applied to one of the resistors 47, 48 or 49, of such polarity that the amplifier voltage causes the control grid of the vacuum tube 60 to become more negative. This voltage will reduce the anodecathode current of the vacuum tube 69, reduce the voltage drop across the resistor 62, increase the positive potential of the terminal 63 with respect to ground and cause a current to flow from the terminal 63 to the terminal 64 through the winding of the relay 42, Fig. 7, operating the relay 42 in one direction. If the applied voltage is of such polarity that the amplifier voltage causes the control grid of the vacuum tube 60 to become less negative, the anode-cathode current of the vacuum tube 90 will increase, increasing the voltage drop across the resistor 62, reducing the positive potential of the terminal 63 with respect to ground and causing a current to flow from the terminal 64 to the terminal 63 through the winding of the relay 42, Fig. 7, operating the relay 42 in the other direction.

A portion of the output of the vacuum tube 54 flows through the voltage dividing resistors 66, 61. A portion of the voltage drop across the resistor 61 is applied by the wire 68 to the control grid of the lower portion of the twin triode 50. A source of voltage 69 has the positive terminal connected to the anode of this portion of the twin triode 50 causing a current to flow from anode to cathode, thence through resistor 52 and source 53 back to source 69. This current flowing in the resistor 52 tends to make the cathode of vacuum tube 50 positive with respect to ground which is equivalent to a negative voltage on the control grid of the upper portion of the twin triode 50. This added voltage is included in the compensation by the source 53 so that normally the control grid of the upper section and the cathode of the twin triode 59 are at ground potential when the two anode currents have reasonable values. The voltage from the resistor 6'! is effectively a negative feedback to the control grid of the upper portion of the twin triode 50. Assume a voltage is applied through one of the resistors 41, 48 or 49 to make the control grid of the upper section of the twin triode more negative. The anode-cathode current of this section will decrease, decreasing the voltage drop in resistor 56, making the control grid of vacuum tube 54 more positive or less negative. The anode-cathode current of vacuum tube 54 will increase, increasing the voltage drop in resistor 19 making the control grid of vacuum tube 60 and the control grid of the lower section of the twin triode 50 less positive or more negative. The anode-cathode current of the lower section of the twin triode 50 will decrease decreasing the voltage drop in the resistor 52, decreasing the positive potential of the cathode, which is equivalent to decreasing the negative potential of the control grid of the upper section of the twin triode 50. Then when the applied signal makes the control grid more negative, the feedback tends to make the control grid less negative and is thus a negative feedback.

It has been shown in United States Patent 2,251,973, August 12, 1941, E. S. L. Beale et al., for example, that the voltage across a capacitor may be proportional to the time derivative or rate of change of the applied voltage. The capacitor H differentiates the applied voltage and feeds back a voltage proportional to the time derivative of the applied voltage which assists in preventing hunting and oscillation of the motor 46, Fig. 7.

The source of voltage 12 supplies voltage through resistor 73 to the potentiometer 14 to adjust the bias voltages applied to the control grids of the vacuum tubes 60 and 50.

Fig. 9 shows a device similar to the device shown in Fig. '7 to produce a rotation of a shaft proportional to the angle 6, Fig. 1. A voltage source 15 is connected across the windings of the potentiometers 1B, 11. A voltage source 18 is connected across the windin of the potentiometer 29, which is also shown in Fig. 6. The windings of the potentiometers I6, 11, 29 have a linear variation of resistance with movement of the wipers. The wiper 19 of potentiometer 18 is moved by the servomotor of the gyroscope maintaining the fixed axis shown in Fig. 1 through the angle x and selects a voltage proportional to The wiper 33 of the potentiometer 29 is moved by the antenna support 23, Fig. 6, through an angle 0 and due to the reversed polarity of source 18, selects a voltage proportional to 0. The potentiometer used in this device may be the potentiometer 29 shown in Fig. 6, or a second potentiometer similarly associated with the antenna support 23. The voltage selected by the wiper is approximately proportional to (0- The voltages selected by the wipers of the potentiometers are supplied to individual input resistors of a summing amplifier 8|, which may be of the type shown in Fig. 8. The voltage in the output of the amplifier 8| will be proportional to +)\0+(0 which should equal zero. If this voltage is not equal to zero, the relay 83 will be operated, starting the motor 82, which moves the wiper 80 of potentiometer 11 to make the voltage from amplifier 8| equal to zero, releasing relay 83 and stopping the motor. The shaft of the motor 82 will then have moved through an angle 0-K, which is equal to the angle 6, Fig. 1.

Thus, from the antenna support 23 of Fig. 6, there is a movement proportional to the angle 6, Fig. 1; from the servomotor of the gyroscope maintaining the fixed axis there is a movement proportional to the angle A, Fig. 1; from the shaft of the motor 82, Fig. 9, there is a movement proportional to 0)\, that is, the angle 6, Fig. 1; and from the shaft of the motor 46, Fig. 7, there is a movement proportional to the horizontal range R, Fig. 2. It is obvious that more than one potentiometer winding may be associated with each of these devices, so that the wipers will be moved proportionately to the particular movement. Also, the servomotors may be geared, or otherwise connected, to the shafts, so that the motor may make more than one revolution for one revolution of the wipers.

In Fig. 11, a source of voltage 9| has its positive pole connected to one end of the winding 92 and its negative grounded pole connected to the other end of the Winding 92. Another source of voltage 93 has its negative pole connected to one end of the winding 94 and its grounded positive pole connected to the other end of winding 94. The windings 92, 94 are preferably segments of the same circle, and have a variation of resistance such as to give a linear variation in voltage. The wipers 95, 96 are moved by the shaft of the motor 46, Fig. '7, but are insulated therefrom and from each other, to select voltages, respectively positive and negative, proportional to the horizontal range, R.

The voltages selected by the wipers 95, 96 are respectively applied to two diametrically opposite points 98, 99 of the potentiometer winding 91. The equidistant, intermediate, diametrically opposite points I00, ll]! of the potentiometer winding 91 are connected to ground. The winding 91 has a resistance varying with length such that the voltage of the winding with respect to ground varies with a sinusoidal function. Assuming zero angle at the point 100 and that the wiper starts at point I00 and rotates clockwise, the voltage of the wiper with respect to ground will be zero at point I 80, positive maximum at point 98, zero at point lfll, negative maximum at point 99, and Zero at point I00 and this is the variation of a positive sine. If the direction of the wiper be turned through 180 degrees, the sign of the sine will be reversed. Thus, the wiper I02, which is turned through 180 degrees will select a voltage varying with the negative sine of the angle of rotation, and the wiper I03, which leads the wiper I02 by 90 degrees will select a voltage varying with the negative cosine of the angle of rotation. The wipers I02, I03 are rotated by the shaft of the motor 82, Fig. 9, through the angle 6, Fig. 1, and are insulated from the shaft and from each other. As the voltage applied to the winding 9! varies with R, the voltage selected by the wiper I02 varies with R sin 5, and the voltage selected by the wiper I03 varies with --R cos 6.

Current from the source 9| can flow through the upper half of the potentiometer winding I04 to ground, thence back to source 9I. Current can also flow from source 93 through ground to the lower half of potentiometer winding I04, thence through connection I05 to source 93. The wipers I06, I01 are simultaneously moved or manually adjusted in opposite directions to select equal positive and negative voltages with respect to ground proportional to the velocity of the vehicle with respect to the air, that is, the air speed S.

The positive voltage from the wiper I06 and the negative voltage from the wiper I0! are applied to diametrically opposite points of a potentiometer winding I08, the equidistant intermediate points being grounded. The potentiometer winding I08 has a resistance varying with the length of the winding such that the voltage with respect to ground varies with a sinusoidal function, and thus has the same variation of voltage with respect to ground as the winding 91. The wipers I I0, III are moved by the shaft of the servomotor of the gyroscope maintaining the fixed axis through an angle proportional to k, the wipers H0, III being insulated from the shaft and from each other. With zero angle at the point I09 and clockwise rotation the wiper IIO will select a voltage proportional to the negative cosine, and the wiper I I I will select a voltage proportional to the positive sine of the angle of rotation. As the applied voltage is proportional to S, the voltage selected by the wiper H0 is proportional to S cos k and the voltage selected by the wiper I II is proportional to +8 sin A.

The resistors H2, H3 limit the currents drawn from the potentiometer winding I04, and thus make easier the design of the potentiometer winding.

In the measurement of the slant range and azimuth angle of the target, some errors are involved. The measuring process is not perfectly accurate, producing random errors in range which are roughly constant but tend to decrease slightly with decreasing range; and random errors in azimuth angle which are in the form of angular errors, but are equivalent to a linear error which also decreases roughly with the reciprocal of the decreasing range. The observers will tend to overrun and underrun the target in tracking, producing a more or less regular error, depending on the skill of the observer, and tending to decrease with decreasing range. As the measurements are expressed in the form of electrical voltages, which are conveniently selected by means of wire-wound potentiometers, there will also be a steplike error due to the sudden variation in voltage from one turn of wire to the next. These small errors in the positional measurements can produce large momentary errors in the derived ratio R and R6, which must be aver 12 aged out. It is difficult to average or smooth an inherently variable quantity, such as R or R6, to produce the most probable value without reducing the accuracy of the measurement. In the present computer, these inherently variable quantities are combined to give quantities which, under the assumptions usually made in bombing, should be constant. In particular, it is assumed that for some time before releasing the bomb, and during the fall of the bomb, the wind and target velocities remain constant in direction and magnitude. Thus, it is convenient and consistent to express R and R6 in terms of the assumed constant velocity of the air with respect to the target. R

and R6 are resolved into components along the X and Y axes. By subtracting the airplanes airspeed components S cos and S sin A, in eifect the air velocity is determined with respect to a point fixed to the target.

The observation of the target may start when the distance is too long for reliable results. Thus, some time after the target has come under observation, the operator presses a key and the observed data are sent to the computer. Observed data are treated as above to give the components of the velocity of the air with respect to the target, and these values are electrically smoothed or averaged. As the earlier observations are not as accurate as the later observations, the avera ing process is weighted approximately in accordance with an inverse range function. This result is attained by switching in added avera ing elements at regular intervals as the range decreases, so that the later observations will have materially more efi'ect on the final result than the earlier observations.

The voltage selected by the wiper I03 proportional to -R cos 6, and the voltage selected by the wiper H0, proportional to --S cos x are supplied to the x wind com uter, Fig. 10: the voltage selected by the wiper I02 proportional to R sin 6 and the voltage selected by the wiper I I I proportional to +5 sin A are supplied to the :1 wind computer, Fi 10.

In Fig. 10 the volta e proportional to S cos it is applied through connection 3I2, resistor I I4, and variable resistor H5, to the amplifier H6, which may be of the type shown in Fig. 13. The resistors I I1, I I8 are connected by connection H9 in serial relationship across the output of the amplifier II 6, and negative feedback is supplied from the junction of resistors H7, H8 through resistor I I5 to the input of amplifier I I6.

The voltage proportional to +5 sin A is similarly applied through connection 3I5, resistor I 20, and variable resistor I2I, to the amplifier I22, which may also be of the type shown in Fig. 13. The resistors I23, I 24 are connected by connection I25, in serial relationship across the output of the amplifier I22, and negative feedback is supplied from the junction of resistors I23, E24 through resistor I2I to the input of amplifier I22.

The voltage proportional to -R cos a is connected through connection 3I3, resistor I26, capacitor I21 and connection I69 to the center armature of relay I28. Similarly, the voltage proportional to -R sin 6 is connected through connection 3M, resistor I29 and capacitor I30 to the right-hand armature of relay I28. At the start of the bombing run, relay I28 is held operated, grounding both of these armatures.

After the bombing run has started and the observationshave settled-down, thekey I3! is operated, releasing the relay I28. When relay I28 is released, the voltage proportional to -R cos 8 is supplied through resistor I26 and capacitor I21 to the input of amplifier I I6; and the voltage proportional to R sin is supplied through resistor I29 and capacitor I30 to the input of amplifier I22. As shown in United States Patent 2,251,973, August 12, 1941, E. S. L. Beale et al., when a voltage is supplied through a capacitor to the input of an amplifier, the output of the amplifier will contain a component proportional to the time derivative, or rate of change, of the applied voltage. Thus, the output of the amplifier II6 will have a component proportional to and the output of the amplifier I22 will have a component proportional to R sins A large value of reverse feedback is supplied by the connections I I9 and I25, thus reducing the apparent input impedances to ground of the amplifiers H6 and I22 to a very low value, increasing the accuracy of the diiferentiating and the summing actions.

The amplifier I I6 adds the applied voltages proportional to -S cos x and and reverses the polarity to produce a voltage proportional to +WX. Similarly the amplifier I 22 adds the applied voltages proportional to and reverses the polarity to produce a voltage proportional to +Wy.

The resistors I26, I29 smooth the applied voltages. The time constants of the resistor I26 and capacitor I21, and of the resistor I29 and capacitor I30 should be fairly small.

The release of relay I28 also connects capacitor I32 and resistor I33 in serial relationship from the output to the input of the amplifier I I6; and connects the capacitor I34 and resistor I35 in serial relationship from the output to the input of the amplifier I22. The feedbacks through capacitors I32 and I34, integrate or average the applied voltages, though, as capacitors I32 and I34 are comparatively small, this averaging is small.

Positive voltage is applied from the source I36, through resistor I31 to a control electrode of the three element cold cathode device I38, which may be a Western Electric type 3130 vacuum tube. As long as the relay I28 is operated, the control electrode is grounded through resistor I39, and the applied voltage is too small to break down the tube. When the relay I28 is released, the voltage from the source I36, through resistor I31, increases the charge on capacitor I40, until the voltage applied to the control electrode breaks down the tube, permitting current from the source I36 and the capacitor I4I to flow through the tube I38 and 'the winding of relay I42, operating relay I42. The resistance of resistor I31, and the capacitance of capacitor I40 are so related to the breakdown voltage of tube I38 that a delay of some ten seconds is produced between the release of relay I28 and the operation of relay I42.

The operation of key I3I and relay I42 completes a locking circuit for relay I42 from the source I43 through the upper springs of key I 3I left make springs and winding of relay I42 to ground; and connects the source I43 through the upper springs of key I 3| and the right make springs of relay I 42 to connection I44.

The grounded wiper I45 is rotated by the shaft of the motor 46, Fig. 7, proportionately to the horizontal range to the target. At some convenient range, the wiper I 45 grounds the contact I46.

When contact I46 is grounded, current can flow from battery I 43, through key I3I, springs of relay I42, connection I44, winding of relay I5I, break contacts of second spring pile-ups of relays I52, I54, I56, I58, I and connection I41 to contact I46, operating relay I5I, which looks up through the middle grounded make contact.

The operation of relay I5I connects capacitor I48 and resistor I49 in parallel relationship with capacitor I32 and resistor I33, increasing the loading function of amplifier I I6; and connects capacitor I6I and resistor I62 in parallel relationship with capacitor I34 and resistor I35, increasing the loading function of amplifier I22.

As the range continues to decrease, the wiper I45 is rotated until contact I 63 is grounded.

When contact I63 is grounded, current can flow from battery I43, through key I3I, springs of relay I42, connection I44, winding of relay I 52, break contacts of second spring pile-ups of relays I53, I55, I51, I59 and connection I64 to contact I63, operating relay I52, which, at the second spring pile-up transfers the chain connection from the winding of relay I5I to the winding of relay I53 and locks up through the grounded make contact of the third pile-up.

The operation of relay I52, at the upper spring pile-up, connects capacitor I65 and resistor I66 in parallel relationship with capacitor I32 and resistor I33; and, at the lower spring pile-up connects capacitor I 61 and resistor I68 in parallel relationship with capacitor I34 and resistor I35.

The continued rotation of wiper I45 causes the operation of the remaining chain relays I53 to I 60, in succession, until the bomb has been released, or minimum range is reached.

The successive operations of the chain relays I53 to I60 connect a succession of capacitors and. resistors in parallel relationship with capacitor I32 and resistor I33, and in parallel relationship with capacitor I 34 and resistor I35, thus progressively changing the averaging properties of amplifiers H6 and I22. The resistors may conveniently be of about 10,000 ohms, capacitors I32, I34 about .1 microfarad each, capacitors I48, IBI about .25 microfarad each and the remaining capacitors, such as I65, I61 about .35 microfarad each.

When the bombing run is completed, the release of key I3I unlocks relay I 42 and all the chain relays I5I to I60 which may be locked up, and operates relay I 28, restoring the circuit to its initial condition in preparation for the next bombing run.

The quantity Wx (and the quantity Wv) is a velocity; thus. the weighted average of this ve locity is, by definition:

By evaluating the time rate of change W: of

Wzfrom the above equation, the equation may be manipulated into the differential form:

WI-WL-KWFQ (10) in which K usually varies with time, and,

l K- -L M Let Cl be the capacitance of capacitor I21, C2 be the capacitance of the capacitors, such as capacitor I32, in the feedback path, R1 be the resistance of resistor II1, the voltage gain of amplifier II6, be large and substantially independent of frequency, the output load of amplifier I I6 be a substantially constant resistance, and the internal output impedence of amplifier II6 be small compared with the resistance R1 in parallel relationship with C2. Under these conditions, the total impedance Zt from the output terminal of amplifier III; to ground is ap-- proximately represented by a capacitance Ct in parallel relationship with a resistance Rt.

The constants of the circuit of Fig. 11 are adjusted to produce scale factors such that the voltage selected by the wiper I03 is K1 R cos 6, and the voltage selected by the wiper H is RzC1 K1 S cos where K1 is a constant.

Including these limitations, the output of amplifier II6, equal to KzWx, obeys the following equation:

The capacitors, such as capacitor I48, are connected to the output circuit of amplifier II6, so that they will be charged up to the output voltage, and are switched, at the low potential side, from ground to the input of amplifier H6, so as to avoid causing spurious discontinuities in the value of Wx.

With 02 increased by discrete steps, the weight function increases exponentially with time between charges, with exponent inversely proportional to the value of C2 and abruptly decreases when a new value of capacity is switched in. These abrupt changes are smoothed out, by the series resistors, such as resistors I26, I29.

The complete circuit produces a result that closely approximates to a weight function which is zero before time to and increases thereafter with the reciprocal of the horizontal range.

The amplifiers H6 and I22 reverse the polarities of the applied voltages. Thus, as the input to the amplifier H6 is proportional to Wx, the

output of amplifier H6 is proportional to +87%;

and the output of amplifier I22 is proportional to +Wy.

The output voltage of amplifier H6 is supplied to the point I 10 of the potentiometer winding I1I, Fig. 11. A portion of the output of amplifier H6 is supplied, through resistor I12, to a summing amplifier I13, which may be of the type shown. in Fig. 13, having a feedback resistor I14. The amplifier I13 reverses the polarity of the applied voltage. The output of the amplifier I13, which is proportional to -Wx is supplied to the point I15 of the potentiometer winding I1I.

The potentiometer winding I1I, like the windings 91 and I08, has a resistance varying with the length of the winding such that the voltage with respect to ground varies with a sinusoidal function. With zero angle at the point I16, and clockwise rotation, the wiper I11 selects a voltage proportional to a negative sine, and the wiper I18 selects a voltage proportional to a positive cosine. The wipers I11, I18 are moved by the shaft of motor 82, Fig. 9, an angle equal to angle 5, Fig. 1, the wipers I11, I18 being insulated from the shaft and each other. The voltage selected by the wiper I11 is thus proportional to Wx sin 5 and the voltage selected by the wiper I18 is proportional to +Wx cos 6.

The output voltage o f the amplifier I22, Fig. 10, proportional to +Wy is supplied to the point I of the potentiometer winding I8I, which has a variation in resistance similar to the variation in resistance of the winding I1I.

The polarity of the output voltage of the amplifier I22, Fig. 10, is reversed in the amplifier I82, which is similar to amplifier I13 and supplied to the point I83 of the winding I8I.

With zero angle at the point I84 and clockwise rotation for increasing angles, the wipers I85 and I86 respectively select voltages proportional to a positive sine and a positive cosine. The wiper I85 is therefore displaced 180 degrees with respect to wiper I11. The wipers I85, I86, like the wipers I11, I18, are moved by the shaft of motor 82, Fig. 9, an amount proportional to angle 6, Fig. 1, and are insulated from the shaft and from each other. The voltage sele lsed by the wiper I85 is thus proportional to +Wy sin a and the voltage selected by the wiper I86 is proportional to +77; cos 8.

The voltages selected by the wipers I06, I91, respectively proportional to +8 and S are supplied, through resistors II2, II3, to points I81, I88 of potential winding I89. The winding I89, like windings 91, I08, HI and IBI, has a resistance varying so as to produce a voltage varying with a sinusoidal function. The wipers I90, and I9I are moved by the support 23, Fig. 6, an amount proportional to the angle 0, Fig. 1. With zero angle at point I92 and clockwise rotation for increasing angle, the wipers I90, I9I respectively select voltages proportional to +8 sin 0 and S cos 0.

The voltage selected by the wiper I11, proportional to W sin 6; the voltage selected by the wiper I proportional to +8 sin 0; and the voltage selected by the wiper I86 proportional to +W cos a are respectively supplied, through resistors I93, I94, I95 to the input of a summing amplifier I96 which may be of the type shown in Fig. 13, having a feedback resistor I91. The summing amplifle r l 96 sums up the voltages +S sin 0 -Wx sin 6 +Wy cos 6, which, from Eq ation 8 are equal to Rt. As the amplifier I96 also reverses the polarity of the applied voltages, the potential of the connection I 9 8 with respect to ground is proportional to -R The voltage selected by the wiper I18, proportional to W x cos 6; the voltage selected by the wiper I9 I, proportional to S cos and the voltage selected by the wiper I85 proportional to +VV sin a are respectively supplied through resistors I99, 200, 20I to a summing amplifier 202, similar to amplifier I56 and having a feedback resistor 203. The annular 202 sums up the voltages S cos s-i-VVE cos ta-W; sin 6, which,

from Equation 7, equal R. Thus, as the amplifier 202 reverses the polarity of the applied voltages, the potential of the connection 203, with respect to ground, is proportional to R.

The connections I98 and 204, Fig. 12, correspond to the similarly numbered connections of Fig. 11.

From Fig. 1 it is evident that, as the vehicle is flying toward the target, the angle 0 cannot exceed plus or minus 90 degrees, because, if the angle 0 exceeds 90 degrees the vehicle would be flying away from the target.

The angle 0 is thus always in the first quadrant, where the sine and cosine are of the same sign, or in the fourth quadrant where the cosine is unchanged, but the sine changes sign. In a potentiometer having only one wiper arm, the winding may extend over the whole circumferthe wiper arm being moved through 20. For a cosine function, the voltages applied to the two halves of the winding are of the same polarity. For a sine function, the voltages applied to the two halves of the winding are of opposite polarity. In a potentiometer having two wiper arms, the winding may extend over the whole circumference, or may be limited to three quadrants extending over the circumference, the arms being geared to rotate through 3/20.

The potentiometer winding 205 has a resistance varying with a cosinusoidal function in the first and fourth quadrants, the zero angle or axis of the vehicle being at the point 206. The wiper 20? is driven by the support23, Fig. 6, at twice the rotational speed of the support 23, say by means of suitable gearing. The' voltage of the connection I98 is applied at the point 206. The voltage selected by the wiper 201 will be proportional to R6 cos 0.

The potentiometer winding 208 has a resistance varying with a sinusoidal function in the first and fourth quadrants, the zero angle being at the ground. The voltage of the connection 204 is applied directly to the upper part of the winding 2%. The voltage of the connection 204 is applied through a resistor 209 to an amplifier 2W, which may be of the type shown in Fig. 13, having a feed back resistor 2. The amplifier 2I0 reverses the polarity of the voltage of the connection 204, and supplies voltage of reversed polarity to the lower half of the winding 208. The wiper 2I2, like the wiper 201, is moved through twice the angle of the support 23, though both Wipers are insulated from the drive and each other. The wiper 2 I2 will select a voltage proportional to R sin 0.

The voltages selected by the wipers 201 and 212 are respectively supplied through resistors 2I3, 2M to an amplifier 2I5 of the type shown in Fig. 14 which adds these voltages and reverses the polarity. The output voltage of amplifier 2I5 tends to be proportional to R6 cos 0+3 sin 0, which is the component of the ground speed V transverse to the course of the airplane.

The output voltage of the amplifier 2 I5 is supplied to the winding of a potentiometer 2I6 having a uniform variation of resistance. The wiper 2I'I is moved by the motor 46, Fig. 7, but is insulated therefrom to select a voltage with respect to ground proportional to the horizontal range R and this voltage is applied through the feedback resistor 2 I0 to the input of the amplifier 2I5.

For simplicity, consider the condition when a. single voltage, E1 is applied, say through the resistor 2I3 to the amplifier 2I5. Let the resistor 2I3 have a resistance R1. Then the input current have a resistance R2. Then the current 12 in the resistor 2! equals REt-E 2 The effect of high negative feedback is to keep Eo=0. Hence, since Let R1=R2, then The output voltage of the amplifier 2I5 is thus of the sum of the input voltages. If the resistors R1 and R2 are not equal, the output voltage is changed in the ratio of R2 to R1. The output voltage is also reversed in polarity.

The output voltage of the amplifier 2I5, proportional to (7? sin 0-1-5005 6) is applied to a potentiometer winding 2I9. The wiper 220 is adjusted to select a voltage propor-- tional to the value of the trail T for the particular speed and altitude of the vehicle. The wiper 220 will thus select a voltage proportional to 65 sin 04-53 cos a This voltage is supplied to the steering circuit 22I, together with a voltage from the connection I98 equal to -Ra.

The steering circuit 22 I, and the amplifier 2I5, shown in Fig. 12, produce a current proportional to the difference of th input voltages 5 sin a+icos a (-133 which may be written E+ E5 cos 0+1 sin 6) as in Equation 1. The output current of the steering circuit 22I actuates the meter .222. When the vehicle is on the correct course, the meter 222 reads in the center of the scale. When 19 the vehicle is off the correct course, the meter 222, which has a center zero, indicates the direction and magnitude of the amount off course. Thus, as the vehicle approaches the release point the pilot steers the vehicle to keep the meter 222 reading zero.

Voltage from the connection 204, Fig. 12, proportional to R,. is applied to the potentiometer winding 223. The wiper 224 is adjusted to select a voltage proportional to the time of fall t for the particular altitude of the vehicle. The voltage selected will be proportional to Rt.

A source of voltage 225 has the negative pole connected to one end of the potentiometer winding 226. The other end of the winding 226 and the positive pole of the source 225 are grounded. The wiper 221 is adjusted to select a voltage proportional to the proper trail T for the speed and elevation of the vehicle. This voltage is applied to the mid-point of the potentiometer winding 228 which is similar to the winding 205. The wiper 229, like the wiper 251, is moved proportionally to the angle 0, and is insulated from the drive shaft. The wiper 229 thus selects a voltage proportional to T cos 0. The wiper 221 and the wiper 220 may be ganged to move simultaneously.

The source of voltage 225 also has the negative pole connected to a potentiometer winding 235. The other end of winding 23!! is grounded. The wiper 23I is moved by the motor 46, Fig. 7, proportionally to the horizontal range to select a voltage proportional to -R. The Wiper 23I is insulated from the drive shaft.

The voltage selected by the wiper 224, proportional to Rt; the voltage selected by the wiper 229, proportional to T cos and the voltage selected by the Wiper 23I, proportional to -R. are respectively supplied, through resistors 232, 233, 234, to the release circuit 235, which may be of the type shown in Fig. 15, and which sums up the applied voltages. The output of the release circuit 235 is thus proportional to R+T cos 0 -351:

Equation 2. When this voltage falls to zero, a relay or latch 236 in the output of the release circuit 235 is released to drop the bomb. A meter may also be connected to the output of the release circuit to indicate the approach to the correct release point.

The summing amplifiers II6, I22 of Fig. I13, I82, I96, 202 of Fig. 11 and 2H), 2I5 of Fig. 12 may all be of the type shown in Fig. 13.

In Fig. 13, the signal voltages are applied to the control grid of the upper section of the twin vacuum tube 240. The source 24I supplies anode current through the coupling resistor 242. The source 243 supplies current to the anode of the lower section, which is connected so as to reduce drift due to variations in cathode activity as described in an article Sensitive D. C. amplifier with A. C. operation, by S. E. Miller, published in Electronics, November 1941, page 27. The combined anode currents flow through the resistor 244, which is of fairly high resistance. The source 245 impresses a potential with respect to ground which opposes the potential due to the voltage drop in the resistor 244. The resistor 244 may be varied to adjust the space currents in the vacuum tube 240.

The control grid of the vacuum tube 246 is directly connected to the anode of the upper section of the vacuum tube 240 and is thus at a positive potential with respect to ground. The cathode 20 of the vacuum tube 246 is therefore connected to the source 243 so that the potential difference between the control grid and cathode of the vacuum tube 246 is of suitable value.

The vacuum tube 246 is coupled to the vacuum tube 241 by an interstage network of the type shown in United States Patent 1,751,527, March 25, 1930, H. Nyquist. The anode circuit is supplied irom the source 24I and the grid bias from the source 245. The vacuum tube 241 is coupled to the vacuum tube 248 by a similar interstage coupling network.

A portion of the output voltage of the vacuum tube 246 is tapped at the point 249 and supplied to the grid of the vacuum tube 250. Thus, the direct signals are supplied to the grid of vacuum tube 256; while vacuum tube 241 acts as a phase inverter and amplifier to supply signals of reversed polarity to the grid of vacuum tube 248.

The control grids of the vacuum tubes 241, 250 are biased to a fairly high negative voltage with respect to ground, and this voltage is largely compensated by a negative bias applied to the cathodes oi the vacuum tubes 241, 256 by the source 25I.

Positive potential from the source 243 is supplied by connection 253 to the anode of vacuum tube 248. The cathode of vacuum tube 248 is connected to terminal 252 and to the anode of vacuum tube 250. The cathode of vacuum tube 250 is connected to the negative pole of the source 25I. The positive pole of source 25I and the negative pole of source 243 are grounded. If the vacuum tubes 248 and 256 have the same anodecathode resistance, and the sources 243, 25I are of the same potential, or if the ratio of the anodecathode resistances of the vacuum tubes 248, 250 is the same as the ratio of the potentials of the sources 243, 25I, these four elements will form a bridge, and in the absence of an applied signal the terminal 252 and ground are conjugate to each other, that is, the terminal 252 is at ground potential.

If a negative signal voltage be applied to the control grid of the vacuum tube 251], an inverted signal will be applied to the vacuum tube 248, the anode-cathode resistance of vacuum tube 250 will increase and the anode-cathode resistance of vacuum tube 248 will decrease, thus unbalancin the bridge and causing a potential to appear at the terminal 252. To counteract the tendency of this potential toward diminishing the response of tube 248, the signal voltage applied to the grid of this tube must be larger than that applied to the grid of tube 256. This condition is brought about by the amplification in the stage which includes tube 241.

The screen grid of tube 248 is connected to source 24I and the screen grid of tube 250 is connected to source 243. The cathodes are heated in known manner (not shown).

Using commercial radio receiving tubes, the source 24I may be about positive 270 volts, the source 245 about negative 270 volts, the source 243 about positive 109 volts and the source 25I about negative volts, all with respect to ground.

A negative voltage applied to terminal 254 will decrease the anode-cathode current of tube 240, decreasing the voltage drop in resistor 242, increasing the positive potential of the control grid of tube 246. Increasing the positive potential of the grid of tube 246'wil1 increase the anode-cathode current, increasing the voltage drop in the coupling resistors, and reducing the positive po- I tential applied to the control grid of tube 241, and

of point 249 connected to the control grid of tube 250. As a reduction of positive potential is equivalent to an increase of negative potential, the variation in potential of the control grid of tube 256 is of the same polarity as the voltage applied to the terminal 254. An increase in negative potential on the grid of tube 241 reduces the anode-cathode current, reducing the voltage drop in the coupling resistors and increasing the positive potential of the grid of tube 248. The increased negative potential on the grid of tube 250 will reduce the anode-cathode current while the increased positive potential on the grid of tube 243 will increase the anode-cathode current; thus, current will flow from terminal 252 through an attached load to round. Thus, if a negative voltage is applied to terminal 254, a positive voltage appears on terminal 252, or the polarity of the applied signal is reversed by the amplifier.

When a feedback resistor is connected between terminal 252 and terminal 254 and a plurality of voltages are applied through individual resistors, as shown, for example, in connection with repeaters I96, 202, Fig. 11, the negative feedback will reduce the apparent input impedance of the repeater to a very low value, so that the various sources do not interact on each other, and the gain of the repeater, for any given source, will be controlled by the ratio of the resistance in the feedback path to the resistance in series with the source.

The resistors 2l3, 2|4, Fig. 12, are connected to terminal 255, Fig. 14, which is connected to the control grid of the lower section of the twin triode 255. The positive pole of a voltage source 251 is applied to the anode of this section. The cathode of the tube 256 is connected through a resistor 258 and a negative voltage source 259 to ground. The control grid of the upper section is connected to ground, and current from a positive voltage source 256 is supplied through resistor 26l to the anode of the upper section. Assume a negative voltage is applied to terminal 255, decreasing the anode current of the lower section and decreasing the voltage drop in resistor 258. The cathode of tube 256 then has a negative potential with respect to ground, which is equivalent to a positive potential on the control grid of the upper section. The lower section of tube 256 thus operates as an inverter to impress on the control grid of the upper section a voltage having a polarity which is reversed with respect to the applied voltage. The polarity is again reversed in the upper section so that the voltage on the grid of the tube 262 is of the same polarity as the signal. This voltage is again reversed by the tube 262 so that the voltage on the grid of vacuum tube 263 is of a polarity reversed with respect to the applied signal.

The cathode of vacuum tube 263 is connected to ground through the potentiometer windings 216, 219, Fig. 12, in parallel relationship.

The negative pole of voltage source 259 is connected through resistor 264 to the cathode of vacuum tube 263. The positive pole of the source of voltage 266 is connected by connection 265 directly to the anode of vacuum tube 263. The positive pole of voltage source 259 and the negative pole of voltage source 260 are grounded.

The resistance of the resistor 264 is selected so that, in the absence of an applied signal, the sources 259, 260, the resistor 264 and the anode cathode resistance of vacuum tube 263 form a balanced bridge; thus point 266 is conjugate with respect to ground and no voltage is applied to windings 2 I 6, 2 l 9.

Assuming a negative voltage to be applied to terminal 255, this will cause a positive voltage to be applied to the control grid of the vacuum tube 263, increasing the anode-cathode current of vacuum tube 263 and unbalancing the bridge. The point 266 will become positive with respect to ground, that is, the wiper 2 I1 will become positive with respect to ground. Wiper 2| 1 is connected by terminal 261, through resistor 2 l8, Fig. 12, to terminal 255 and the control grid of vacuum tube 256. Thus, a negative voltage with respect to ground applied to the control grid of vacuum tube 255 produces a voltage on wiper 2I1 which is positive with respect to ground, and this voltage is applied to the same control grid, forming a reverse or negative feedback.

The unbalance voltage between the point 266 and ground, due to a Voltage applied to terminal 255, is also applied to the potentiometer winding 219, shown in Fig. 12. The voltage selected by the wiper 229 is applied to the control grid of vacuum tube 268.

The voltage from the connection I98, Fig. 12, is applied through terminal 269 to the control grid of a vacuum tube 219.

Positive voltage from the source 260 is supplied by connection 255 through resistors 21l, 212 to the anode of vacuum tube 268; and through resistors 213, 214 and meter 215 to the anode of vacuum tube 210.

The cathodes of vacuum tubes 268, 210 are connected through resistor 216 and a negative voltage source 211 to ground and the negative pole of source 269. The anode-cathode resistances of the vacuum tubes 268, 210 with the resistors 21l, 212, 213, 214 and meter 215 form a bridge which, in the absence of a signal voltage, is balanced. The meter 215 has a center zero for normal value of anode current in vacuum tube 210 and this zero may be accurately set by adjusting resistor 214.

Assuming that vacuum tubes 268 and 210 are of the same type, having the same mutual conductances and internal impedances; that the product of the mutual conductance of a tube and the internal impedance are large compared to unity; that the product of the mutual conductance of a tube and the resistance of resistor 216 are also large compared to unity; that the resistance of resistors 21l, 212 equals the resistance of resistors 213, 214, and is large compared to the internal impedance of the tubes, then, it may be shown that the unbalance voltage sending current through 213, 214, and meter 215 equals Where g is mutual conductance of tubes,

R1 is internal impedance of tubes,

R is resistance of resistors 2H and 212, V1 is voltage applied by wiper 220,

V2 is voltage applied by terminal 2 69.

The current through meter 215, and the output voltages developed across resistors 21!, 213, thus are proportional only to the difference between the voltages applied to the signa1 grids of the vacuum tubes 268, 210, and are not appreciably afiected by equal voltages applied to these grids,

23 The voltage applied by the wiper 229 is proportional to 65 cos 9+R sin and the voltage from connection I98, Fig. 2,

applied to terminal 269 is proportional to -R6. These voltages are equal, and vary equally, when the airplane is flying on the correct track, and the needle of the meter 215 reads in the center. If these voltages are not equal, then the needle of the meter 215 will be deflected from zero.

The release circuit, designated 235 in Fig. 12, is shown in detail in Fig. 15. The resistors 232, 233, 234, Fig. 12, are connected to terminal 289 of Fig. 15, terminal 28! being grounded. The voltage applied to the control grid of the upper section of vacuum tube 282 is thus proportional to and this negative voltage on the control grid of vacuum tube 282, reduces the anode current of vacuum tube 292 to a small value. The anode current of vacuum tube 282 is supplied by voltage source 293 through the anode coupling resistor 284. The lower section of the twin triode vacuum tube 282 is connected like the lower section of vacuum tube 249, Fig. 13, to compensate for cathode temperature drift.

The voltage applied to terminal 238 is amplified by the upper sections of the twin triode vacuum tubes 282, 281 and supplied to the control electrode or the gas-filled triode 289. A positive voltage from the source 299 is applied to the cathode of the gas-filled triode 289, to produce a negative bias on the control electrode. The negative bias from the source 299, with the negative amplified signal, holds the tube 289 inoperative until the amplified signal falls to zero, reducing the negative bias on the control electrode of the gas-filled triode 289 and permitting the tube to fire.

Current from the source 283 is supplied by connection 29L key 292 and resistor 293 to charge capacitor 294'. When the gas-filled tube 289 fires, the capacitor 294 discharges through the relay or latch winding 236 and tube 289, energizing the winding 239 and releasing the bomb. The discharge of capacitor 294 permits current to flow from source 283 through resistor 293, causing a voltage drop across resistor 293 which lights a small neon lamp 295, or other indicator, to indicate the release of the bomb. Upon completion of the bombing run, when the control electrode of the gas-filled triode 289 is again biased negatively, the key 292 is operated, breaking the circuit from the source 283 and permitting the tube 289 to restore.

The voltage applied to the terminal 289 releases the bomb when Rt-T cos 0 R=0, which is the correct release condition, but if no precautions were taken, the bomb might be released when the airplane was not headed properly. The steering circuit of Fig. 14A is arranged to block the bomb release circuit of Fig. 15 as all times when the airplane is of: the correct track.

The anodes of a double diode vacuum tube 296 are connected to the outer ends of the resistors 211, 213, Fig. 14A. The outer ends of two equal resistors 291, 219 are also connected respectively to the anodes of tube 296. The junctions of resistors 291, 219 are connected through resistor 298 to the cathode of tube 296.

When the airplane is on the correct track, equal voltages are applied to the control electrodes of vacuum tubes 268, 219, and assuming the resistances of resistors 212, 214 are equal and the resistances of resistors 2'", 213 are equal, equal voltages are applied to the anodes of tube 296. As the resistors 291, 219 are equal, no current flows in tube 296. When the airplane is off the correct track, the voltages applied to the control grids of the vacuum tubes 268, 219 are not equal, and the anode-cathode currents are not equal. Assume the anode-cathode current of tube 268 to decrease while the anode-cathode current of tube 219 increases. The decreased current in resistor 21! will permit the positive potential of the outer end of resistor 21l to rise, while the increased current in resistor 213 will cause the positive potential of the outer end of resistor 213 to fall. Current can then flow from the lower anode of tube 296 to the cathode and through resistors 298, 291.

Similarly, when the anode-cathode current of tube 268 increases while the anode-cathode current of tube 219 decreases, then current can flow from the upper anode of tube 296 to the cathode and through resistors 298, 219. Thus, whenever the airplane is off the correct track, the cathode of tube 296 and the free end of resistor 298 become more positive with respect to ground. This potential will appear on terminal 299., which is connected to terminal 399, Fig. 15.

Terminal 399 is connected through resistor 39! to a resistor 392 connected to the control electrode of the lower section of the twin triode 281. The negative pole of the voltage source 288 is also connected through resistor 393 to resistor 392. The potential of source 288 is selected so that, when the airplane is on course, the anode-cathode current of tube 281 is small. When the airplane is on course, the positive potential developed across resistor 298, Fig. 14A, is applied through resistors 39!, 302 to the control electrode of the lower section of tube 281, and causes the anode-cathode current of tube 281 to increase.

The source 299 is connected through the winding of relay 394 to the anode of the lower section of tube 281. When the airplane is on course, the anode-cathode current of tube 281 is too small to operate relay 394. When the airplane is ofi the correct track, this anode current increases, operating relay 394 and connecting negative voltage from the source 285 to the control grid of the gas-filled triode 289, preventing the triode 289 from firing and releasing the bomb. Thus, even if the release voltages have fallen to the correct value, the bomb cannot be released, unless, at the same time, the airplane is on the correct track.

What is claimed is:

1. In a system for indicating the course to be fiown by an aerial vehicle to drop a bomb on a target, a first source of voltage, computing means connected to said sotu'ce and controlled by observations of said target to produce first and second voltages respectively proportional to the components normal to the vertical plane through said vehicle and said target and normal to said course, of the horizontal speed of said vehicle relative to said target, means connected to said computing means for fractionating said second voltage proportionally to the ratio of the trail of said bomb to the horizontal range to said target, first and second vacuum tubes, each having anode, cathode and control grid, the control grid of said first tube being connected to the source of said first voltage, and the control grid of said second tube being connected to said fractionating means, a first resistor, connected to said cathodes, a second grounded source of voltage having the negative pole connected to said first resistor, a first pair of resistors respectively connected to said anodes, a third grounded source of voltage having the positive pole connected to said pair of resistors, and a meter connected in series with one of said pair of resistors.

2. The combination in claim 1 with a second pair of resistors respectively connected in serial relationship to said anodes, a duo-diode having its anodes connected to taps in said first pair of resistors and a cathode, a second resistor connected from the junction of said second pair of resistors to the cathode of said duo-diode, a circuit for releasing said bomb including a gasfilled device having a control electrode, a source of negative voltage, and relay means connected to the cathode of said duo-diode and operated by an unbalance voltage from said second resistor to connect said source of negative voltage to the control electrode of said gas-filled device.

3. In a computer. a source of energy, mechanism connected to said source and controlled by observations of the location of a target with respect to a bomber to produce a first quantity of energy proportional to the component of the ground speed of the bomber normal to the vertical planethrough the bomber and the target and a second quantity of energy proportional to the horizontal component of said ground speed normal to the axis of the bomber, means connected to said mechanism to fractionate said second quantity of energy proportionally to the ratio of the trail of a bomb relative to said target and the horizontal range to said target, means connected to said mechanism and said fractionating means for comparing said first and said fractionated ouantities and ind cating their difference. whereby when said difierence is zero, the bomber is on the correct course to drop a bomb on sa d target.

4. In a com uter, a source of volta e, mechanism connected to said source and control ed by observations of the location of a target with respect to a bomber to produce a first voltage proport onal to the com onent of the ground s eed of the bomber normal to the vertical plane through the bomber and the target and a second volta e proportional to the horizontal component of the ground speed normal to the axis of the bomber. means connected to said mechanism to fractionate said second vo ta e pronortiona l to the ratio of the trail of a bomb relative to said target and the horizontal ran e to said target, a meter circuit connected to sa d mechanism and sa d fractionating means for comparing the magnitudes of said first and said fractionated voltages and indicating their difference, whereby when said difference is zero, the bomber is on the correct course to drop a bomb on said tar get.

5. In a com uter, a source of voltage, mechanism connected to said source and controlled in accordance with observations of the location of a target with res ect to a bomber to produce a first voltage proportional to the component in the vertical plane through the bomber and target of the relative horizontal velocity of the bomber and target and a second voltage proportional to the component of said velocity normal to said plane and including a shaft rotated proportionally to the azimuth angle between the axis of the bomber and said plane, polarity reversing means connected to the source of said first voltage, a first potentiometer having a winding varying in resistance with a sinusoidal function connected to the source of said first voltage and to said means and a first brush rotated by said shaft to select a third voltage proportional to the positive sine of said azimuth angle, a second potentiometer having a winding varying in resistance with a cosinusoidal function connected to the source of said second voltage and a second brush rotated by said shaft to select a voltage proportional to the positive cosine of said azimuth angle, summing means connected to both said brushes to add said third and fourth voltages, fractionating means connected to said summing means to fractionate the sum of said voltages proportionally to the ratio of the trail of a bomb relative to said target and the horizontal range to said target, and a meter circuit connected to the source of said second voltage and said fractionating means for comparing the magnitudes of said voltages and indicating their difierence, whereby when said difference is zero, the bomber is on the correct course to drop a bomb on the target.

6. In a computer, a source of voltage, mechanism connected to said source and controlled by observations of the location of a target with respect to a bomber to form the source of a first voltage proportional to the component of the ground speed of the bomber normal to the vertical plane through the bomber and the target and a second voltage proportional to the horizontal component of the ground speed normal to the axis of the bomber, means connected to said mechanism to fractionate said second voltage proportionally to the ratio of the trail of a bomb relative to said target and the horizontal range to said target, a pair of vacuum tubes, each having cathode, anode and control grid, said cathodes being connected together and said grids being respectively connected to the source of said first voltage and said means, a pair of resistors in serial relationship connected to said anodes, a source of power connected to said cathodes and the junction of said resistors, and a meter connected in serial relationship with one of said resistors.

7. The combination in claim 6 with a second pair of resistors in serial relationship connected to said anodes, a duo-diode having its anodes respectively connected to the anodes of said vacuum tubes and a cathode, a resistor connected from the cathode of said duo-diode to the junction of said second pair of resistors, a circuit for releasing said bomb including a gas-filled device having a control electrode, a source of negative voltage, and relay means connected to the cathode of said duo-diode and operated by an unbalance voltage from said resistor to connect said source of negative voltage to said control electrode to prevent the release of the bomb.

CHARLES H. TOWNES. DEAN E. WOOLDRIDGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,573,850 Naimann Feb. 23, 1926 2,119,607 Sterba June 7, 1938 2,290,091 Brown et al July 14, 1942 2,292,159 Richardson Aug. 4, 1942 2,317,419 Taylor et a1 Apr. 27, 1943 2,407,325 Parkinson Sept. 10, 1946 

